A new study published Sunday by the journal Nature Climate Change concludes the much-debated Keystone XL pipeline could produce four times more global warming pollution than the State Department calculated this year.
The proposed pipeline would carry oil from tar sands in western Canada to Texas, passing through western Nebraska.
Researchers estimate it would increase world carbon by as much as 121 million tons a year compared with the department's estimate of 30 million tons. Study lead author Peter Erickson says the government calculations didn't take into account that the added oil from the pipeline would drop prices. That would spur consumption, which in turn would mean more pollution.
Supporters say other studies indicate the pipeline would not pose an environmental threat and not impact U.S. greenhouse gases.